JPH10199695A - Inverter type x-ray high voltage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform exposure of an X-ray in an ideal tubular voltage waveform with less distortion to be provided for diagnosis in an inverter type X-ray high voltage device provided with a tubular voltage feedback control device by employing a digital control method, and changing control gain in the middle of X-ray exposure. SOLUTION: A device comprises a rectifier circuit 1, an inverter 2, a high voltage transformer 3, and a high voltage rectifier 4. In this case, an inverter input voltage and a tubular voltage are detected, these plural control quantities are A/D converted to be operated for comparison with target control values inputted through an operation panel and an included MPU, result of operation is D/A converted to be supplied through a gate control circuit of an SCr to control the rectifier circuit 1, and through a drive circuit to control the inverter circuit 2, and control gain is changed by preset software during X-ray exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an AC power supply,
It is converted to direct current, this direct current is converted to high frequency alternating current using an inverter, the output voltage is boosted by a high voltage transformer, and then rectified again to generate a high direct current voltage. The present invention relates to an inverter type X-ray high voltage device that emits X-rays when applied.

[0002]

2. Description of the Related Art FIG. 4 shows a basic configuration of an X-ray tube voltage control system of a conventional inverter type X-ray high voltage apparatus. X in the figure
The tube voltage applied to the tube 6 is controlled by adjusting the operation phase difference, frequency, pulse width and the like of the inverter 2. The voltage converted to high frequency by the inverter 2 is
Utilizing a resonance phenomenon between the capacitor 18 and the leakage inductance of the high-voltage transformer 3, the high-voltage transformer 3 boosts the voltage to a high voltage. Is applied to the X-ray tube 6. Note that the high-voltage cable 5 has a capacitance,
This has the effect of smoothing the tube voltage.

[0003] The tube voltage control circuit 21 includes an actual tube voltage Vx detected by the tube voltage detector 8 and a set target tube voltage signal which is input from a not-shown input device such as a console or the like. Vr is compared with the first comparison means 10, and parameters such as the operation phase difference, frequency, pulse width, etc. of the inverter 2 are obtained by various correction means described later, and the detected tube voltage Vx is compared with the target tube voltage signal Vr. It is controlled so as to match. Although the control of the tube current is not shown in FIG. 4, the temperature of the filament of the X-ray tube 6 is adjusted by the tube current control circuit 26 in FIG. 1 to control the amount of thermoelectrons emitted from the filament. By doing.

In the above X-ray high voltage device, the tube voltage Vx
When the tube voltage rises (transient state) in the process of approaching the target value from zero volts, an extremely large current flows because the capacitance of the high-voltage cable 5 is charged. In the time domain in this transient state, most of the diodes constituting the high-voltage high-voltage rectifier circuit 4 are in a conductive state for the most part of the time domain. On the other hand, in the steady state after the tube voltage has risen, the diode conducts only when the input voltage of the high-voltage rectifier circuit 4 is higher than the tube voltage. The load state on the secondary side of the high-voltage transformer 3 is significantly different from that at the time of startup. Conventionally, in this type of inverter type X-ray high voltage apparatus, as shown in a tube voltage control circuit 21 in FIG. 4, the tube voltage is controlled by PID (proportional, integral, differential) control. In the circuit 21, before the X-ray irradiation, respective control gains Kp (proportional gain) and Ki suitable for the load condition are set.
(Integral gain) and Kd (differential gain) were set and the same control gain was used from the start to the end of X-ray exposure, and these were not actively switched. Control for switching the control gain during X-ray irradiation was, of course, difficult in analog control, and was not performed in digital control. This is because, as will be described later, the inverter frequency has recently been increasing, but conventionally, when the operating frequency was not so high, the pulsation in the steady state (determined by the operating frequency) was originally large, so the control gain was switched. Even so, no remarkable effect could be expected due to the influence of pulsation. Therefore, according to the conventional control method, the same control gain is used for two states having different properties, that is, at the time of rising of the tube voltage (transient state) and at the steady state. The control conditions were not met and an ideal tube voltage waveform could not be obtained.

In recent medical X-ray apparatuses, high-precision, reproducible, large-current, short-time control is required for X-ray high-voltage apparatuses in order to take sharp X-ray pictures with high diagnostic performance. It is required to apply a tube voltage waveform that rises at a high speed and has no pulsation in a steady state. In addition, high-speed rise and fall of the tube voltage are also strongly demanded at the same time in order to improve the photographic effect and reduce the exposure to soft X-rays. Therefore, the operating frequency of the inverter is increasing. FIG. 5 shows a comparison between an ideal tube voltage waveform and an actual tube voltage waveform. Under the circumstances described above, in the normal X-ray high-voltage device, the control gain is determined by giving priority to a high-speed response having no overshoot and a short rise time as shown in FIG. Was normal. Therefore, in the conventional steady state, a compensating control gain has to be set to some extent, so that a satisfactory waveform is often not obtained, and improvement of this point has been desired.

[0006]

In the above-mentioned conventional apparatus, the control gain in the tube voltage control circuit 21 is set to the same value as described above for two states having different properties of a transient state and a steady state. Therefore, there is a problem that an ideal tube voltage waveform cannot be obtained, for example, pulsation increases in a steady state. Hereinafter, these problems will be described in detail.

When the X-ray irradiation conditions such as the tube voltage value, the tube current value, and the irradiation time are set by a console (to be described later) that controls the operation of the entire high-voltage device, the tube voltage control circuit 21 is configured as shown in FIG. As shown in FIG. 4, the comparison means 10 compares the target tube voltage signal Vr obtained from the tube voltage set value with the actual tube voltage Vx detected by the tube voltage detector 8, and integrates the difference as a tube voltage deviation. Means 11 performs integral control. PID (proportional control) is performed by adding the integral control and the proportional control mainly by the proportional adjusting means 12 for suppressing the overshoot at the rising of the tube voltage and the differential control mainly by the differential adjusting means 13 for suppressing the pulsation in the steady state. , Integral, derivative) control. The value of the gain (integral gain Ki) of the inner integral control has a large effect on the rise time, and the larger the value, the faster the rise tends to be, and also plays a large role in stabilization in a steady state. Fulfill.

In an ordinary X-ray high-voltage device, as described above, it is desirable to determine a control gain that is desirable for the rise time by giving priority to the fact that there is no overshoot in the rise time waveform and that the rise time is fast. It was normal. The control gain determined in this manner is not always an optimum control gain for a steady state having a different characteristic from the rising transient state. In many cases, a waveform could not be obtained. On the other hand, when the integral gain Ki is increased to reduce the pulsation in the steady state, the tube voltage often overshoots at the rise as shown in FIG. This phenomenon indicates that the optimum integral gain at the time of rising is often insufficient compared with that of the steady state. However, depending on the load condition, conversely, it may be desirable to make the integral gain at the steady state smaller than the integral gain at the rise.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a medical X-ray medical system by setting an optimal control gain for each operation at a rising tube voltage and a steady state in different operation states.
It is an object of the present invention to provide an inverter type X-ray high voltage device capable of obtaining a tube voltage waveform close to an ideal required for a wire device.

[0010]

According to the present invention, there is provided a rectifier circuit for receiving and rectifying an AC power supply, an inverter for converting the DC output voltage to a high-frequency AC, and a high-voltage converter for boosting the output voltage of the inverter. A voltage transformer, a high voltage rectifier circuit for rectifying the output of the high voltage transformer and applying the rectified output to an X-ray tube, and a tube voltage detector for a target tube voltage signal Vr inputted and set via an operation console And a tube voltage control circuit that controls the inverter so that the actual tube voltage Vx detected in the step (b) matches the X-ray high voltage apparatus according to claim 1. In particular, a configuration is provided that includes a gain switching unit that can switch the gain of the control loop. According to the second aspect, the switching unit switches the control gain between when the X-ray irradiation rises and when the X-ray irradiation is steady. According to a third aspect of the present invention, the inverter input voltage in the control loop, X
The calculation for controlling the tube voltage and the like is converted into a digital quantity via an A / D converter to calculate control conditions including switching of the control gain, and the calculation result is converted into an analog quantity by the D / A converter. The object is achieved by having a digital control circuit for controlling the X-ray tube operating conditions such as the rectifying circuit, the inverter, the X-ray tube cathode heating and the anode driving conditions after the reconversion.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an entire configuration of an inverter type X-ray high voltage apparatus to which the present invention is applied. This X-ray high voltage device
The DC voltage from the rectifier circuit 1 is converted into a high-frequency voltage using an inverter 2, and the output high-frequency voltage is converted to a high-voltage transformer 3.
Then, the DC voltage is rectified by a high-voltage rectifier circuit 4 and the obtained DC voltage is supplied to an X-ray tube 6 via a high-voltage cable 5 to emit X-rays. A voltage to be applied to the X-ray tube 6 is detected by an inverter input voltage detector 7 and a tube voltage actually applied to the X-ray tube is detected by a tube voltage detector 8, and a tube current Ix and a tube voltage Vx, which will be described later. Although not shown, a tube voltage control circuit 21 (a shaded portion in FIG. 1) via a control signal input unit 27 for calculating a control condition from a correlation with
Is input to an internal A / D converter and converted into a digital value, and is then controlled to a predetermined condition by an X-ray control circuit 9 based on a digital control method inserted into a feedback loop.

Next, the functions of the main components will be described. The rectifier circuit 1 is a device that supplies a DC voltage. The rectifier circuit 1 rectifies the voltage of a 50 Hz or 60 Hz AC commercial power supply (single-phase or three-phase) with a rectifying element such as a diode and smoothes an inductance L and a capacitor C. A DC voltage is obtained by smoothing with an element. The inverter 2 receives the DC voltage output from the rectifier circuit 1, converts the DC voltage into a high-frequency voltage, and controls the voltage (hereinafter, tube voltage) output to the X-ray tube. The high-voltage transformer 3 boosts the high-frequency voltage from the inverter 2, and its primary winding is connected to the output side of the inverter 2 via a capacitor 18. The high-frequency output voltage from the secondary winding of the high-voltage transformer 3 is supplied to the high-voltage rectifier circuit 4, and the rectified output voltage is applied to the X-ray tube 6 through the high-voltage cable 5 and is applied to the X-ray tube 6. Radiate. The input voltage signal Vi of the inverter 2 detected by the inverter input voltage detector 7 is converted into a digital signal by an A / D converter built in the tube voltage control circuit 21, and then a control signal calculation process is performed. It is. Further, the tube voltage detector 8 outputs an inverter control signal S to the inverter 2 in an output circuit 28 in the X-ray control circuit 9 via a control signal input unit 27 for determining a control signal from a correlation with the tube current Ix. At the output side of the high-voltage rectifier circuit 4 and at the connection to the input side of the X-ray tube 6. The above description is about the tube voltage, but the tube current control circuit 26 similarly sets the target tube current and the tube current detector 1 for the tube current.
Control is performed so that the actual tube currents detected at 9 match.

The tube voltage control circuit 21 includes a microprocessor unit (MP) mounted on a console 22.
U), the target tube voltage signal Vr, the inverter input voltage signal Vi detected by the inverter input voltage detector 7, and the tube voltage signal V detected by the tube voltage detector 8.
x and a comparison operation, and similarly, the tube current detector 19
, A tube current Ix is detected, a detection signal is compared with a target tube current Ir generated by a microprocessor unit (MPU) mounted on the console 22 in the same manner as described above, and the exposure of the X-ray tube 6 is performed. The control signal S and the gate signal G to the rectifier circuit 1 are sent to the inverter 2 so that the emission condition becomes a predetermined condition. In FIG. 2, the control signal supplied to the tube voltage control circuit 21 through the tube voltage input wiring a may be only the tube voltage Vx as described above, but the correlation between the tube current Ix and the tube voltage Vx may be obtained. Is calculated by the control signal input unit 27 and the calculated value is used.
However, among the above controls, the tube current control can be omitted in some cases.

Next, the configuration and function of the tube voltage control circuit 21, which is a main part of the present invention, will be described in detail with reference to FIG.
In this embodiment, although not shown for controlling the tube voltage, a microcontroller including an A / D converter on input wirings a and b and a D / A converter on output wiring c is applied. ing. In a tube voltage control circuit 21 for performing digital feedback control by software using a microcontroller, a first comparing means 10, an integral adjusting means 11, a proportional adjusting means 1 shown in FIG.
2. The functions of the differential adjusting means 13, the second comparing means 14, the input voltage correcting means 15, the steady-state characteristic correcting means 16 and the like are all processed in digital quantities. Therefore, the input signals of the tube voltage input wiring a and the inverter input voltage wiring b in FIG. 2 are both analog signals, and although not shown, the input voltage correction means connected to these input wirings a and b respectively. 15. An A / D converter provided immediately before the differential adjusting means 13 and the proportional adjusting means 12 converts the digital quantity into a digital signal and supplies the digital signal from the control signal output line c. After being converted into an analog amount by a D / A converter provided on the output side of the inverter 16, the operation of the inverter 2 is controlled through the output wiring c. A control gain in a transient state at the start of X-ray irradiation and control in a steady state by a microprocessor unit (MPU) mounted in a tube voltage control circuit 21 forming a feedback loop shown in FIG. Performs gain switching. That is, in the present invention, by configuring the X-ray control circuit 9 using the digital feedback system as described above, the control gains of the integral adjusting means 11, the proportional adjusting means 12, and the differential adjusting means 13 in FIG. The gain switching means 17
To switch between the rise of the tube voltage and the steady state,
It is characterized in that it has a function of freely selecting the optimal control gain for both of them according to the X-ray irradiation conditions.

Next, the specific operation of the digital feedback control of the tube voltage control circuit 21 of the inverter type X-ray high voltage device having the above-described configuration and function will be described with reference to FIG.
This will be described with reference to FIG. First, preparation for X-ray irradiation starts when an X-ray irradiation request is issued. That is, the irradiation conditions such as the tube voltage, the tube current, and the irradiation time, and the gain setting of each of the integral, proportional, and derivative control units are performed. For example,
Regarding the tube voltage, the target tube voltage signal Vr input from the console 22 and obtained by the arithmetic processing by the MPU 23 for X-ray control, and the tube voltage signal Vx converted into a digital quantity
Are compared with each other by the tube voltage control circuit 21, and the processing of the first comparing means 10 in FIG. 2 is performed to calculate the difference between the two. Next, this calculation result is subjected to calculation processing in the tube voltage control circuit 21 such as the differential adjustment means 13 and the proportional adjustment means 12 in FIG. 2, and is compared with the calculation result of the integration adjustment means 11. The calculation result is processed by the input voltage correction means 15 in FIG. 2 together with the inverter input voltage signal Vi detected by the input voltage detector 7. That is, the result of the comparison operation includes the inverter input voltage signal V
The variation of the input voltage is corrected by multiplying the reciprocal of i. Thus, the tube voltage feedback accompanying the X-ray irradiation operation is started, and at the same time, the measurement of the time from the start of the irradiation is also started. When the measured time reaches a preset rise time, the gain is switched to an optimal gain for a steady state. Here, the corrected operation result is further input to the steady-state characteristic correction means 16 and subjected to correction processing in consideration of the output characteristics of the device. All of the above processing is performed by software in the tube voltage control circuit 21. As a result of this processing, an inverter control signal S for controlling the operation of the inverter 2 is generated in the output circuit 28 including the phase difference pulse circuit and the D / A conversion circuit. The inverter control signal S determines the switching timing of each switch of the inverter 2 according to the target tube voltage signal Vr. As a result, the inverter 2 converts the DC voltage output from the rectifier circuit 1 into an AC voltage, which is sent to the high-voltage transformer 3 and boosted, then rectified by the high-voltage rectifier circuit 4 into a DC voltage, and X A high-voltage DC voltage is applied to the wire tube 6.

Next, the operation of switching the gain in the tube voltage control circuit 21 of the present invention having the above-described configuration, function and operation will be described. Here, as an example, a case where the integral gain is switched after the tube voltage rises is considered. Integral value Si in integral adjusting means 11
Is the integrated value from the start of X-ray emission to the time (time T) of the value obtained by multiplying the value obtained by subtracting the detected tube voltage Vx from the target tube voltage signal Vr by the integral gain Ki, that is,

[0018]

(Equation 1)

## EQU1 ## The switching of the integral gain can be easily realized because digital control by software is used. For example, in addition to the method based on the above-described time measurement, when the tube voltage reaches the target value, the integral gain is switched, or the rise time is 1 ms.
Therefore, there is a method of performing a process of switching Ki when the irradiation time exceeds 1 ms while observing a software timer. This can be easily achieved by incorporating the algorithm shown by the flowchart in FIG. 3 into the control program.

In the same manner as above, for example, a DSP
A controller without a built-in A / D converter, such as a digital signal processor, can also be used. In this case, the software may be configured such that an A / D converter for A / D converting the inverter input voltage signal Vi from the inverter input voltage detector 7 and the tube voltage signal Vx from the tube voltage detector 8 is added. This object can be achieved by digital control according to.

In the above embodiment, the control gain is divided into two stages, that is, a rising stage and a steady stage, and the optimum gain is set. However, this stage is further subdivided and the gain is increased many times. You may switch. Further, in the tube voltage control circuit 21, as in the case of FIG.
However, the present invention is not limited to this, and the present invention is not limited thereto, and may be a combination of any two of the three adjusting means, or only one of the integral adjusting means 11 and the proportional adjusting means 12. Is also good. Similarly, in the above-described embodiment, the control data acquired by the A / D conversion is the inverter input voltage Vi, the tube voltage Vx, and the tube current Ix. Omitting the tube current detector for detecting (tube current) may be practically acceptable.

In the above embodiment, digital control is applied. However, even when analog control is used, for example, when switching of an integral gain is performed, a capacitor of an integrator using an operational amplifier is used. The above-described invention can be realized by providing means for switching at a predetermined time.

On the other hand, the rectifier circuit 1 only needs to generate a DC voltage, and is not limited to the above configuration. For example, a battery may be used without using a commercial power supply. Further, even when a large output power is obtained, when the voltage drop is small, or when a change in the input voltage may affect the output voltage (tube voltage), the acquisition of the input voltage and the input voltage correction means are omitted. <You can also. Further, in the above description, the high-voltage cable 5 is used in all cases, but the above-described invention can be applied to a so-called one-tank type in which the high-voltage transformer 3 and the subsequent units are integrated. Similarly, in FIG. 1, a resonance capacitor 18 is shown connected to the output side of the inverter 2. However, this capacitor 18 has a high frequency current due to the leakage inductance of the high voltage transformer 3. It is inserted for the purpose of improving that the current does not sufficiently flow through the winding of the voltage transformer 3, and is not necessarily inserted when the above-described improvement is not necessary.

[0024]

As described above, according to the present invention, the digital arithmetic processing is performed in the feedback loop, and the gain switching means is provided in the digital processing process, so that it becomes necessary during the X-ray irradiation. It is possible to freely set an optimal control gain in accordance with the above, thereby providing an inverter type X-ray high voltage device capable of obtaining a tube voltage waveform close to an ideal required for a medical X-ray device. Become.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an inverter type high-voltage device showing an embodiment of the present invention.

FIG. 2 is a signal processing configuration diagram of a voltage control circuit according to the present invention.

FIG. 3 is a flowchart of signal processing software according to the present invention.

FIG. 4 is a system diagram showing an X-ray tube voltage control system in a conventional device.

FIG. 5 is an ideal waveform diagram and an actual waveform diagram of a tube voltage in a medical X-ray apparatus.

FIG. 6 is a waveform diagram when an overshoot occurs when a tube voltage rises.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 rectifier circuit 2 inverter 3 high voltage transformer 4 high voltage rectifier circuit 5 high voltage cable 6 X-ray tube 7 inverter input voltage detector 8 tube voltage detector 9 X-ray control device 10 First comparing means 11 ... Integral adjusting means 12 ... Proportional adjusting means 13 ... Differential adjusting means 14 ... Second comparing means 15 ... Input voltage correcting means 16 ... Stationary characteristic correcting means 17 ... Gain switching means 18 ... Series resonant capacitor 19 ... tube current detector 21 ... tube voltage control circuit 22 ... console (MPU) 23 ... X-ray control MPU 24 ... gate circuit 25 ... drive circuit 26 ... tube current control circuit 27 ... control signal input unit 28 ... output circuit

Claims (3)

[Claims] A rectifier circuit for receiving an AC power supply and rectifying the same, an inverter for converting the DC output voltage into a high-frequency AC, a high-voltage transformer for boosting the output voltage of the inverter, and a high-voltage transformer A high-voltage rectifier circuit for rectifying the output of the detector and applying the rectified output to the X-ray tube; and a tube voltage control circuit for inputting a target tube voltage and controlling the inverter so that the actual tube voltage of the X-ray tube matches the actual tube voltage. An inverter type X-ray high voltage apparatus comprising: a tube voltage control circuit including means for switching a gain of a control loop during an X-ray irradiation operation in a control loop. Line high voltage equipment. 2. The gain switching means of the control loop for controlling the X-ray exposure condition includes dividing at least two time regions in accordance with a lapse of time from a rise of the tube voltage, and 2. An inverter type X-ray high voltage apparatus according to claim 1, further comprising means for switching and setting a predetermined gain for the apparatus. 3. A control loop for controlling the X-ray exposure condition includes an A / D converter for converting an inverter input voltage detection signal and an X-ray tube voltage detection signal, which are analog quantities, into digital quantities, and Each signal obtained by processing the converted digital signal by a built-in microprocessor is compared with an irradiation condition set by a console, and a control signal for controlling the rectifier circuit, the inverter, and the X-ray irradiation condition is determined in advance. An X-ray control circuit generated by software configured by a set program, and a control signal for supplying the digital signal to a rectifier circuit, a gate circuit for controlling the operation of each circuit of an inverter, and a drive circuit. 2. An inverter type X-ray high voltage apparatus according to claim 1, wherein the circuit comprises a circuit including a D / A converter for converting into an analog quantity.